A method and a circuit for channel estimation of the related technique will be described with reference to the drawings. FIG. 11 depicts a block diagram showing an arrangement of a conventional channel estimation device.
Referring to FIG. 11, a wireless unit 902 converts an RF signal received over an antenna 901 into a baseband signal. A CP removing unit 903 removes a CP (Cyclic Prefix) region of the received signal. An initial stage FFT unit 904 performs discrete Fourier transform, using an OFDM (Orthogonal Frequency Division Multiplexing) symbol as a unit. An RS/data separation unit 905 separates an FFTed signal into RSs (Reference Signals) and data in accordance with a wireless frame format. A channel estimation unit 906 calculates transfer characteristics of a channel between sending and receiving devices based on the RSs. A demodulation unit 907 calculates soft decision bit values from the received data using a channel estimation value. An error correction/decoding unit 908 performs error correction/decoding on the soft decision bit values to restore a transmission bit sequence.
FIG. 12 depicts a block diagram showing an arrangement of the channel estimation unit 906 in a conventional channel estimation device. Referring to FIG. 12, an RS waveform shaping unit 919 converts RS symbols into a format suited to IFFT calculations. An RS signal generation unit 926 generates complex conjugates of an RS symbol sequence. A multiplication unit 920 performs complex multiplications to output the result of the calculations. An IFFT unit 921 performs inverse Fourier transform with N_IFFT points. A noise path removing unit 922 calculates the power of an input signal from one RS number to the next. If the power calculated is greater than a noise threshold value Nth, the noise path removing unit outputs the input signal per se and, if otherwise, the noise path removing unit outputs 0+j·0. An FFT unit 924 performs FFT calculations on the output signal of the noise path removing unit.
In Patent Document 1, there is shown a receiving device of the OFDM system, in which an estimated channel value of each sub-carrier high in accuracy may be obtained even in case the number of sub-carriers is not a power of 2. This is made possible by optimally carrying out noise removal of a delay profile obtained by IFFT processing of the estimated channel value of each sub-carrier.    [Patent Document 1]    JP Patent Kokai Publication No. JP-P2005-045628A